Surface modification process of quartz glass crucible

ABSTRACT

A process for modifying the surface of a quartz glass crucible and a modified quartz glass crucible produced by the process, where the crucible has a transparent coated layer containing a crystallization accelerator on the surface. The process includes coating a mixed solution containing a metal salt and a partial hydrolyzate of alkoxysilane oligomer on the surface of the crucible and heating to obtain a quartz glass crucible having a transparent coated layer. The crystallization accelerator contains a metal oxide or a metal carbonate dispersed in a silica matrix.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a surface modification processof a quartz glass crucible and to a surface modified quartz glasscrucible which is used in the process of pulling up silicon singlecrystal used for a semiconductor etc. from molten silicon.

[0003] 2. Discussion of the Background

[0004] As one of the causes that a dislocation is formed in siliconsingle crystal in the pulling method, it has been known thatcristobalite formed on the inside surface of the quartz glass crucibleis released into the molten silicon. As a countermeasure to this, aprocess is known in which an alkaline earth metal is coated on an insidesurface of the crucible to act as a crystallization accelerator. Themetal forms a cristobalite layer on the inside surface of the crucibleat an early stage of pulling tip (e.g. U.S. Pat. No. 5,976,247, JapanesePatent No. 3,100,836). In these inventions, a barium hydroxide solutionis coated on the surface of the quartz glass crucible and the coatedbarium hydroxide reacts with carbon dioxide in air to form bariumcarbonate on the surface of the crucible. The barium carbonate is weaklyadhered on the surface of the crucible by drying and is used as acrystallization accelerator.

[0005] However, quartz glass crucibles surface-treated by conventionalmethods have the following problems and improvements are desired. Thatis, (A) since the barium carbonate powder on the quartz glass crucibleis not fixed with any binder, the adhesion strength of the powder isvery weak so that the powder is easily abraded and falls off whencontacted by persons and instruments. Such abrasion occurs in theproduction process of the crucibles, such as product inspection,conveyance, and insertion to a carrying case, etc. It also occurs in theuser's process, where the quartz glass crucible is set on a carbonsusceptor in the pulling up equipment. As a result, its adhesion statebecomes non-uniform and spot-like. Furthermore, there is also apossibility that worker health is negatively affected because bariumcarbonate powder is scattered when the carrying case is opened. (B)Since the adhesion strength of powder is very weak, nucleationefficiency as a crystallization accelerator is low, and so the amount ofbarium carbonate required becomes excessive. (C) If the crucible iswashed, the barium carbonate powder adhered on the surface of thecrucible is washed away. It is then impossible to wash the crucibleafter the adhesion of the barium carbonate powder, even if some soilsadhere on the surface of the crucible.

SUMMARY OF THE INVENTION

[0006] The present invention solves the problems of the conventionalquartz glass crucible and provides a surface modified quartz glasscrucible having a transparent coated layer which is not abraded uponcontact with handling instruments or persons, has sufficient durability,and also provides its surface modification process.

[0007] That is, the present invention relates to the following surfacemodification process of the quartz glass crucible.

[0008] [1] A surface modification process of a quartz glass crucible,the process comprising, coating a mixed solution, (hereinafter referredto as the silica sol liquid), containing a metal salt and a partialhydrolyzate of alkoxysilane oligomer on the surface of the crucible,burning said coated solution to form a transparent coated layercontaining a crystallization accelerator derived from the metal salt inthe silica matrix.

[0009] The surface modification process of the present inventionincludes the following processes.

[0010] [2] The surface modification process of a quartz glass crucible,wherein the metal salt is a metal organic acid salt or a metal carbonateof one or more kinds of magnesium, calcium, strontium, or barium.

[0011] [3] The surface modification process of a quartz glass crucible,the process comprising, coating the silica sol liquid on the whole or apart of the inside and/or outside of the surface of the quartz glasscrucible, and burning said coated silica sol liquid.

[0012] [4] The surface modification process of the quartz glasscrucible, wherein the silica sol liquid has 0.01 to 15 weight % of metalcontent, which is calculated as an oxide, and 0.5 to 30 weight % ofsilicon concentration, which is calculated as SiO₂, is used.

[0013] [5] The surface modification process of the quartz glasscrucible, the process also comprising, drying the silica sol liquid, andburning said dried liquid at 350 to 1200° C. for 10 to 120 minutes.

[0014] In addition, the present invention also relates to the followingquartz glass crucible.

[0015] [6] A quartz glass crucible, having a transparent coated layer,in which the crystallization accelerator is dispersed in the silicamatrix, on the whole or a part of the inside and/or outside surface ofthe crucible.

[0016] The quartz glass crucible of the present invention includes thefollowing crucibles.

[0017] [7] The quartz glass crucible, wherein the crucible is made by,coating the silica sol liquid containing the metal salt and the partialhydrolyzate of alkoxysilane oligomer on the surface of the crucible, andburning the coated silica sol liquid to form a transparent coated layercontaining the crystallization accelerator derived from the metal saltin the silica matrix.

[0018] [8] The quartz glass crucible, wherein the crucible is made bycoating the silica sol liquid containing a metal organic acid salt or ametal carbonate of one or more kinds of magnesium, calcium, strontium,or barium, on the surface of the crucible, and burning coated silica solliquid to form the transparent coated layer containing the metal oxideor the metal carbonate as the crystallization accelerator.

[0019] [9] The quartz glass crucible used as the crucible for pulling upsilicon single crystal.

[0020] The surface modified quartz glass crucible of the presentinvention has a hard and transparent coated layer, in which the metaloxide or the metal carbonate is dispersed in a silica matrix, on thewhole or a part of the inside and/or outside surface of the crucible. Inaddition, the metal oxide or metal carbonate acts as a crystallizationaccelerator to the surface glass layer of the crucible at the hightemperature of pulling up the silicon single crystal. Therefore, whenthe crucible is used for pulling up silicon single crystal, a uniformcristobalite layer is formed on the inside surface of the crucible at anearly stage of pulling up, and as a result a high dislocation free ratioof the pulled crystal can be obtained. Moreover, the strength of thecrucible under a high temperature is increased by the uniformcristobalite layer formed on the inside or outside surface of thecrucible.

[0021] Moreover, since the coated layer is integrated structurally tothe surface of the crucible by baking, it is very stable and has highdurability. Therefore, there is no abrasion when contacted withinstruments or persons and no problem that the adhesion state of themetal oxide in the coated layer becomes to non-uniform. In addition, thedislocation free ratio of silicon can be increased, since a uniformcristobalite layer is formed on the surface of the crucible at pullingup the single crystal even if the coating layer is comparatively thin.On the other hand, regarding the conventional quartz glass cruciblehaving the adhered barium carbonate powder on its surface, since theadhesion strength of the barium carbonate powder is very weak, it can bewashed away easily by acid washing. Therefore, it is impossible to washthe crucible even if impurities are adhered on the surface of thecrucible. While regarding the surface modified quartz glass crucible ofthe present invention, since the coated layer is baked on the surface ofthe crucible, it is not washed away by acid washing. Impurities on thesurface of the crucible can be removed easily by acid washing to preventthe contamination of the silicon single crystal by such impurities togreat an extent as possible.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereafter, the present invention is explained concretelyaccording to the preferred embodiment.

[0023] The surface modification process for producing the quartz glasscrucible of the present invention is a formation process for atransparent coated layer on a surface of a crucible, where acrystallization accelerator is dispersed in a silica matrix. Moreover,the quartz glass crucible of the present invention has a transparentcoated layer on the whole or a part of the inside and/or outside surfaceof the crucible. The crystallization accelerator is a metal compoundexcept for silica, which is for example a metal oxide or metalcarbonate. Concretely, the metal is for example, magnesium, calcium,strontium, or barium etc.

[0024] The transparent coated layer, where the crystallizationaccelerator is dispersed in the silica matrix, can be formed by coatingthe mixed solution (the silica sol liquid) containing the metal salt andthe partial hydrolyzate of alkoxysilane oligomer on the surface of thecrucible, and by burning this coated silica sol liquid.

[0025] The silica sol liquid forming the transparent coated layer is amixed solution which contains both a metal salt and a partialhydrolyzate of an alkoxysilane oligomer as components. The metal salt isfor example a salt of magnesium, calcium, strontium, or barium, which isa useful metal as a crystallization accelerator to accelerate theformation of the cristobalite layer on the surface of the quartz glasscrucible. In addition, a silica sol liquid containing a stabilizingreagent can also be used. The preferred metal salt is a metal organicacid salt or a metal carbonate.

[0026] The most preferable metal organic acid salts are carboxylates. Asan acyloxy group to form the carboxylate, the materials indicated by thegeneral formula C_(n)H_(2n+)COO, where n is an integer of 3 to 7, arepreferable. Concretely, the acyloxy group derived from n-butyric acid,α-methyl butyric acid, iso-valerie acid, 2-ethyl butyric acid,2,2-dimethyl butyric acid, 3,3-dimethyl butyric acid, 2,3-dimethylbutyric acid, 3-methyl pentanoic-acid, 4-methyl pentanoic acid, 2-ethylpentanoic acid, 3-ethyl pentanoic acid, 2,2-dimethyl pentanoic acid,3,3-dimethyl pentanoic acid, 2,3-dimethyl pentanoic acid, 2-ethylhexanoic acid, or 3-ethyl hexanoic acid, etc., can be used suitably.

[0027] Moreover, when a β-diketone, such as 2,4-pentanedione(=acetylacetone), 3-methyl-2,4-pentanedione,3-isopropyl-2,4-pentanedione, or 2,2-dimethyl-3,5-hexanedione etc., ismixed with said carboxylate solution, the preservation stability of theliquid is improved.

[0028] It is preferable that these organic acid salts are dissolved inan organic solvent. As the suitable organic solvent, an ester and/or analcohol, or a mixed solvent, where the carboxylic acid is further mixedwith an ester and/or an alcohol, can be used. As the ester of theorganic solvent, ethyl acetate, propyl acetate, n-butyl acetate,sec-butyl acetate, tert-butyl acetate, iso-butyl acetate, n-amylacetate, sec-amyl acetate, tert-amyl acetate, and iso-amyl acetate, arepreferable.

[0029] As an alcohol, methanol, ethanol, 1-propanol, 2-propanol,1-butanol, 2-butanol, iso-butyl alcohol, 1-pentanol, 2-pentanol,2-methyl-2-pentanol, and iso-amyl alcohol, etc., are suitable. Inalcohols, an alkoxy alcohol, i.e., the alcohol containing an ethergroup, is included. For example, 2-methoxyethanol and 1-methoxy-2-propanol can be used.

[0030] As another example of a usable solvent, a ketone, such asacetone, methylethylketone, and methyisobutylketone, and a hydrocarbon,such as toluene, xylene, hexane, and cyclohexane, can be used. It ispossible that a mixture of two and more kinds of these organic solventsis used. The solution containing a carboxylate of a metal is mixed withthe solution containing the partial hydrolyzate of an alkoxysilaneoligomer, to provide the predetermined composition, and the silica solliquid is prepared. The silica sol liquid has high wettability to thesurface of the crucible. The final hard and transparent silica coatedlayer, in which the metal oxide is dispersed in the silica matrix, can,be formed by burning to dehydrate said silica sol liquid after theorganic components are removed completely.

[0031] The partial hydrolyzate of an alkoxysilane oligomer used in thepresent invention is obtained by a process in which the alkoxysilaneoligomer is hydrolyzed under the controlled reaction conditions, andafter the alcohol is removed, each generated OH group is bonded togetherto form the silica sol. As a suitable starting material, one or moresilane compounds having at least one, preferably more than two, and morepreferably more than three alkoxyl groups, can be used. Concretely,tetraethoxysilane (=ethylsilicate), tetrapropoxysilane,methyltriethoxysilane, dimethylmethoxysilane, phenyltriethoxysilane,chlorotrimethylsilane, various kinds of silane coupling reagents, suchas vinyltriethoxysilane, y-aminopropyltriethoxysilane, etc., also can bementioned. Ethylsilicate, which is the cheapest and to be easilyhydrolyzed, is preferred.

[0032] These alkoxysilanes are used as the hydrolyzate, which ispartially hydrolyzed beforehand. The partial hydrolysis is carried outin the presence of an acid catalyst, i.e., an inorganic acid, such ashydrochloric acid, or an organic acid, such as p-toluene sulfonic acid,and water. Then, the reaction conditions, including, whether using theacid catalyst or not, the amount of acid catalyst, the amount of thewater for hydrolysis in the reaction system, the reaction temperatureand the reaction time, are adjusted to obtain the partial hydrolyzate ofalkoxysilane oligomer, where the degree of polymerization is controlled.It is preferable that the partial hydrolysis is carried out with heatingand stirring in an organic solvent containing water. In addition, it ispreferable that the reaction temperature is 30 to 60° C., morepreferably 35 to 55° C., and the reaction time is 2 to 5 hours.

[0033] Regarding the metal amount in said silica sol liquid, it ispreferable that the metal amount in the coated layer is 1×10⁻⁹ to 1×10⁻⁶mol/cm², per unit area, which is calculated as an oxide, when the coatedsilica sol liquid is baked to form said coated layer on the surface ofthe crucible. For example, it is preferable that the metal content ofthe silica sol liquid is 0.01 to 15 weight %, preferably 0.5 to 10weight %, which is calculated as an oxide, and the silicon concentrationis 0.5 to 30 weight %, which is calculated as SiO₂. The solutioncontaining the metal salt and the partial hydrolyzate solution ofalkoxysilane oligomer, are mixed and prepared to provide the preferablemetal content and silicon concentration. When the metal content is lessthan 0.01 weight %, which is calculated as an oxide, a repeat coating isnecessary to nucleate the crystal sufficiently on the surface of thecrucible to form the desired devitrification layer thickness. On theother hand, when the content is more than 15 weight %, it is difficultto make a stable mixed solution. Moreover, when the siliconconcentration is less than 0.5 weight %, which is calculated as SiO₂,the strength of the formed coated layer is not sufficient, and when theconcentration is more than 30 weight %, it is difficult to make themixed solution stable. It is preferable that the silicon concentrationis 0.5 to 30 weight %, more preferably 1 to 20 weight %.

[0034] As the method for coating the silica sol liquid on the surface ofthe crucible a spray method and a dipping method, etc. can be used, andthe coating method is not limited. In addition, the silica sol liquid onthe surface of the crucible can be coated on a part or the whole of theinside surface or can be on a part or the whole of the outside surface;or can be on a part or the whole of both inside and outside surfaces. Inorder to increase the dislocation free ratio of the single crystal bythe crystallization acceleration effect with the metal oxide duringpulling up of the crystal, the silica sol liquid must be coated on atleast the whole or a part of the inside surface of the crucible.

[0035] The silica sol liquid is coated on the surface of the crucibleand is burned. It is suitable that the burning temperature is 350 to1200° C., preferably 600 to 1000° C. and the burning time is 10 to 120minutes. When the burning temperature is less than 350° C., the strengthof the coated layer is not sufficient, and when said temperature is morethan 1200° C., there is a possibility that the coated layer isdenitrified. By this burning, the silica component of the silica solliquid forms the hard silica matrix. Moreover, regarding the silica solliquid containing the metal organic acid salt as the metal salt, themetal organic acid salt is decomposed into the metal oxide and thetransparent coated layer in which the metal oxide is uniformly dispersedin the silica matrix, is formed on the surface of the crucible. Burningincludes heating and/or oxidation and does not require that combustionof an organic component take place.

[0036] On the other hand, regarding the quartz glass crucible containingthe metal carbonate, when the burning temperature is more than thedecomposition temperature of the metal carbonate, the coated layer,where the metal carbonate is decomposed to the metal oxide to dispersein the silica matrix, is formed. On the other hand when the burningtemperature is less than the decomposition temperature, the coatedlayer, where the metal carbonate is dispersed in the silica matrix ametal carbonate, is formed. In addition, when the burning temperature isnear the decomposition temperature of the metal carbonate, the coatedlayer, where the metal oxide decomposed from a part of the metalcarbonate and the non-decomposed metal carbonate are mixed, can beformed.

EXAMPLE 1

[0037] Preparation of a partial hydrolyzate of an alkoxysilane oligomer.Two kinds of a partial hydrolyzate of alkoxysilane oligomer of (I) and(II) were prepared at the mixing ratios of raw materials and thereaction conditions, shown in Table 1.

EXAMPLE 2 Preparation of the Silica Sol Liquid

[0038] (2-1) 13.8 g of 2-ethylhexanoic barium (C₇H₁₅COO)₂Ba wasdissolved in a mixed solvent of 60 g of iso-amyl alcohol and 26.2 g ofiso-amyl acetate to make a 5 weight % solution, which was calculated asBaO. Next, 20 g and 50 g of the partial hydrolyzates of alkoxysilaneoligomer shown in Table 1 (I), were added and mixed with 20 g, 40 g, and50 g of the solutions respectively. Furthermore, in the liquid A and theliquid B, 1-butanol was added to adjust the concentrations. Then, thesilica sol liquids of A, B, and C shown in Table 2 were prepared.

[0039] (2-2) 24.0 g of 2-ethylbutyric barium (C₅H₁₁COO)₂Ba was dissolvedin a mixed solvent of 70 g of 1-butanol and 6 g of acetylacetone, andrefluxed to make 10 weight % solution, which was calculated as BaO.Next, 40 g and 80 g of the partial hydrolyzates of alkoxysilane oligomershown in Table 1 (II) were added to mix with 20 g and 50 g of thesolutions respectively. Furthermore, in the liquid D, iso-amyl alcoholwas added to adjust the concentration. Then, the silica sol liquids Dand E shown in Table 2 were prepared.

[0040] (2-3) 0.5 g of barium carbonate powder having an average particlesize of 1 μm was dispersed in 100 g of a partial hydrolyzate ofalkoxysilane oligomer shown in Table 1 (I) to prepare the silica solliquid F in Table 2. In the reaction vessel for the preparation, theequipment having the stirring propeller was used to prevent theprecipitation of the barium carbonate powder.

EXAMPLE 3 Formation of the Coated Layer

[0041] Five kinds of the silica sol liquids, (A-E), shown in Table 2,were sprayed to coat the surfaces of quartz glass crucibles for pullingup the single crystal, and the coated layers were formed by burning thecoated liquids at 850° C. for 30 minutes, wherein the crucibles weremade by an arc fusion with rotating mold method, which is generally usedin the process to produce the crucible for pulling up a single crystal.

[0042] In this case, the quartz glass crucibles were surface treated byusing the liquids F and H. Sample No. 6 was made by spaying the silicasol liquid F to coat the surface of the crucible to be burned at 850° C.for 30 minutes. In addition, Sample No. 8 was made by a conventionalcoating method. That is, the liquid H, where barium hydroxideoctahydrate was mixed with water, in which the mixing ratio is 3 g ofbarium hydroxide octahydrate in 11 of water, was sprayed on the crucibleto heat at 300° C. with carbon dioxide gas.

EXAMPLE 4 Strength of the Coated Layer

[0043] The mechanical strength of the coated layer formed by using theliquids A, F, and H, shown in Table 2, was evaluated according to thespecification standard (JIS 5600-5-4). This evaluation was done using ascratching method with a marketed pencil (trade name Mitsubishi UNI).The results are shown in Table 3. Regarding the coated layer formed byusing the liquid A of the present invention, the strength of the layerwas high since the layer was glassy, and scratching did not appear withthe pencil. Moreover, regarding the coated layer formed by using theliquid F, although the barium carbonate powder was contained, the silicacomponent became a binder, so that the strength of the layer was high,and scratching did not appear with a pencil. On the other hand,regarding the coated layer formed by using the conventional liquid H,scratching appeared using a pencil of 3H hardness. From these results,it was confirmed that the coated layer of the present invention hadremarkably stronger mechanical property than the conventional layer.

EXAMPLE 5 Washing Test

[0044] Washing tests were carried out on the quartz glass crucibles,(No. 1, 6, 8) in Table 2, which, were coating treated. The tests wereconducted on the following processes. (1) Washing with pure water anddrying. (2) Washing with pure water and drying after washing with dilutehydrochloric acid. The adhesion amounts of the residual barium on thesurface after each washing test, are shown in Table 3. Regarding thequartz glass crucible of the present invention (No. 1), barium was notremoved, and the adhesion amounts were not changed in the water washingprocess (1) and the acid washing process (2). Moreover, regarding thequartz glass crucible of the present invention (No. 6), although theform of barium was the sodium carbonate, which was same as theconventional, one, since the barium carbonate was dispersed in thesilica sol liquid and coated to burn, the coated silica became thepreservation layer. So the barium was not removed in the washing process(1) and the acid washing process (2) like the quartz glass crucible (No.1). On the other hand, regarding the conventional quartz glass crucible(No. 8), since the barium carbonate was not baked, the barium was washedaway a little in the water washing process (1), and the barium carbonatewas washed away completely in the acid washing process (2).

EXAMPLE 6 Test of the Dislocation Free Ratio

[0045] The pulling up tests of the silicon single crystal were carriedout by using quartz glass crucibles having transparent coated layers(No. 1 to No. 5), and the quartz glass crucible where the bariumcarbonate powder was dispersed in the partial hydrolyzate of thealkoxysilane oligomer (No. 6). The dislocation free ratio of the pulledcrystals, are shown in Table 4. Moreover, for the comparison, the samepulling up tests were also conducted on quartz glass crucible (No. 7),in which the surface was not modified and there is no crystallizationaccelerator layer on its surface and to the quartz glass crucible (No.8), in which the crystallization accelerator layer was formed by aconventional method. The dislocation free ratios of the single crystalare shown in Table 4. In addition, the thickness of the crystallizationlayer of the crucible after pulling up the single crystal was measured.The thickness of the crystallization layers is shown in Table 4. Asshown in the results in Table 4, regarding the quartz glass crucible ofthe present invention, the crystallization layers having the sufficientlayer thickness were formed on the surface of the crucible also withcomparatively a little amount of barium, and a high dislocation freeratio could be obtained. On the other hand, regarding the quartz glasscrucible of the comparative example No. 7, the dislocation free ratiowas remarkably low. Moreover, regarding the quartz glass crucible of thecomparative example No. 8, where barium carbonate was adhered by theconventional method, although this quartz glass crucible has the almostsame adhesion amount of barium as used of the present invention, thecrystallization layer after pulling up the single crystal was thin inthe crucible, and the dislocation free ratio was remarkably low.

EXAMPLE 7 Burning Temperature

[0046] The silica sol liquid (No. 1) shown in Table 2 was sprayed tocoat the surface of a quartz glass crucible for pulling up the singlecrystal, and a coated layer was formed by baking said coated liquid atthe temperatures shown in Table 5 for 30 minutes. The mechanicalstrength of the coated layer was evaluated according to thespecification standard (JIS 5600-5-4). This evaluation was carried outusing the scratching method with a marketed pencil (trade nameMitsubishi UNI). Furthermore, washing tests were also conducted. Thewashing tests were carried out by measuring the adhesion amount of theresidual barium on the surface after washing with pure water and drying.Moreover, for comparison, the same tests were conducted on a quartzglass crucible which was not burned after coating. These results areshown in Table 5.

[0047] As shown by these results, regarding the coated layer baked at atemperature of more than 600° C., scratching did not appear when using apencil of hardness 6H, and the adhesion amount of barium in the coatedlayer after washing was not changed. In addition, regarding the coatedlayer baked at 400° C., although the thin trace of the scratching wassometimes appeared with a pencil of hardness 6H, cracking did not appearwith a pencil of hardness 5H, and the decreased adhesion amount ofbarium by washing was remarkably low. On the other hand, regarding thecoated layer baked at 200° C., since the baking was not sufficient,scratching appeared with a pencil of hardness 3H, and the adhesionamount of barium decreased to less than half by washing. In addition,regarding the coated layer, which was not baked, since the layer wassoft due to being in the gel state, scratching appeared using a pencilof hardness 2B easily, and the coated layer was almost washed away inthe washing test due not being baked.

EXAMPLE 8 Multi-Pulling Test

[0048] Regarding the quartz glass crucible having the coated layer shownin No. 3 in Table 2, the multi-pulling test was done, in which thepulling up of silicon single crystal was repeated by charging thepolysilicon into the crucible again after pulling up the single crystal.In addition, recharging was done without lowering temperature. Theseresults are shown in Table 6. Moreover, the result of the comparativetest by the conventional quartz glass crucible having the bariumcarbonate powder, (No. 8) in Table 2, is also shown in Table 6.

[0049] Regarding the quartz glass crucible having the coated layer ofthe present invention (No. 3), the crystal layer was formed uniformly onthe inside surface of the crucible with the crystallization acceleratorcontained in the coated layer, and the releasing of cristobalite wasstopped. Therefore, even when the pulling up of a single crystal wasrepeated 4 times, a high dislocation free ratio, which was the level of80%, was kept. As a result, the crucible life was prolonged. On theother hand, regarding the conventional quartz glass crucible havingweakly adhered barium carbonate powder, (No. 8) in Table 2, thecristobalite was deposited non-uniformly and partially as the pulling upwas repeated. Then, the frequency of the release of cristobalite to themolten silicon increases so that the dislocation free ratio wasdecreased gradually. In addition, regarding the crucible, in which thepulling up the single crystal was repeated 4 times, the cristobalitelayer was not identified on the surface of the crucible. By the way,regarding the conventional quartz glass crucible having the adheredbarium carbonate powder (No. 8), it is necessary that the amount ofadhered barium is more than 20 μm/g for obtaining the multi-pullingeffect, which was the same as the present invention. When such an amountof barium is adhered on the surface of the crucible, it cannot beavoided to give the bad influence to the quality of the single crystalsilicon.

EXAMPLE 9 Other Crystallization Accelerator

[0050] 2-ethylhexanoic acid salts of Mg, Ca, and Sr were added to thepartial hydrolyzate of the alkoxysilane oligomer shown in Table 2 (I) toprepare a silica sol liquid. The silica sol liquid was sprayed to coat aquartz piece having 10 cm square, and the transparent coated layer wasformed by burning said coated liquid at 850° C. for 30 minutes. Theadhesion amount of the metal was adjusted, so that it became 1 μg/cm²,which was calculated as an oxide. Next, the transparent coated layer wasput into an electric furnace to bake at 1450° C. for 5 hours in argongas at 1 atmosphere pressure. Then, it was confirmed that the uniformcrystallization layer could be formed by also using all said metals.

Effect of the Invention

[0051] A quartz glass crucible has a transparent coated layer containinga crystallization accelerator on the surface, and since the coated layerforms an integrated structure to the surface of the crucible, there isno abrasion, and the adhesion state of a crystallization accelerator,such as barium, contained in the coated layer, is kept uniformly.Therefore, the cristobalite formation on the surface of the crucible atthe pulling up the single crystal is completely uniform, so that anexcellent dislocation free ratio can be obtained. Moreover, there is noproblem that the coated layer is abraded in contact with the handlinginstruments or persons, in the working process after making thecrucible, during from the inspection to the shipment, and the workingprocess in the user side of the crucible. In addition, there is noconventional problem that the fine barium carbonate powder is scatteredwhenever the case containing the crucible is opened. TABLE 1 Oligomer(I) Oligomer (II) Starting Raw Material and Ethylsilicate 40Ethylsilicate 40 Used Amount 150 g 67.5 g Solvent and Used AmountEthylalcohol 400 g Ethylalcohol 1.1 g Catalyst and Used Amount 60%concentra- 60% concentra- tion of Nitric tion of Nitric acid 0.6 g acid0.7 g Additional Amount of 45 g 36.4 g Water Reaction Temperature and45° C. - 3 hours 45° C. - 3 hours Time Silica Solid Part About 10 wt. %About 25 wt. %

[0052] TABLE 2 Silica Sol Liquid Adhesion BaO SiO₂ Amounts of No. KindsOligomer Solutions Containing Metal Salt Dilution Alcohol AmountsAmounts Metal Oxide 1 A (I)  20 g  5 wt. % Calculated as BaO 20 gButanol 60 g 1 2 0.6 2 B (I)  20 g  5 wt. % Calculated as BaO 40 gButanol 40 g 2 2 0.8 3 C (I)  5 g 10 wt. % Calculated as BaO 50 g — 5 51 4 D (II)  40 g 10 wt. % Calculated as BaO 50 g Isoamyl 10 g 5 10 5.2 5E (II)  80 g 10 wt. % Calculated as BaO 20 g — 2 20 9.5 6 F (I) 100 gCarbonic Acid Ba Powder 0.5 g — 0.4 10 2.1 7 G Non-Surface Treatment 0 8H Conventional Ba Carbonate Powder 1

[0053] TABLE 3 Sample No. 1 6 8 Silica Sol Liquids A F H Hardness ofCoated Layer No Cracking No Cracking Cracking (Hardness by Pencil) by 6Hby 6H Appeared by 3H Ba Amount Before Washing 0.6 2.1 1.0 (1) Ba AmountsAfter Water 0.6 2.1 0.3 Washing and Drying (2) Ba Amounts After Acid 0.62.1 0 Washing, Water Washing, and Drying

[0054] TABLE 4 No. 1 2 3 4 5 6 7 8 Rates of Single 81 83 85 83 80  81 3555 Crystallization % Crystallization 80 77 83 95 90 103  0 10 LayersAfter Pulling up μm

[0055] TABLE 5 Burning Temperature Non-Burning 200° C. 400° C. 600° C.800° C. 1000° C. Hardness of Coating Cracking Cracking No Cracking NoCracking By 6H Layer Appeared by Appeared by by 5H 2B 3H Washing Test BaAmounts Before 0.6 0.6 0.6 0.6 Washing Ba Amounts After 0 0.2 0.5 0.6Washing and Drying

[0056] TABLE 6 Rates of Single Crystallization % Number of Times ofPulling up 1 2 3 4 Coated Crucible (No. 3) 85 85 83 83 ConventionalCrucible Having 55 50 47 42 Ba Carbonate Powder (No. 8)

[0057] Japanese application 2001-318032, filed on Oct. 16, 2001 isincorporated herein by reference in its entirety.

[0058] Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed is:
 1. A process for modifying a surface of a quartzglass crucible, said process comprising, coating a silica sol liquidcomprising a metal salt and a partial hydrolyzate of an alkoxysilaneoligomer on said surface of said crucible, and heating said cruciblecoated with said silica sol liquid to form a transparent coated layercomprising a crystallization accelerator derived from said metal salt.2. The process of claim 1, wherein the metal salt is a metal organicacid salt or a metal carbonate-of one or more of magnesium, calcium,strontium, or barium.
 3. The process of claim 1, wherein the silica solliquid is coated on a part of an inside and/or outside surface of thequartz glass crucible.
 4. The process of claim 1, wherein the silica solliquid comprises 0.01 to 15 weight % of metal content, based on anoxide, and 0.5 to 30 weight % of silicon concentration, based on SiO₂.5. The process of claim 1, further comprising, drying the coated silicasol liquid, and heating said dried silica sol liquid at a temperature offrom 350 to 1200° C., for 10 to 120 minutes.
 6. The process of claim 1,wherein the metal organic salt is a carboxylate of formulaC_(n)H_(2n+)COO, where n is an integer of from 3 to
 7. 7. The process ofclaim 6, wherein the metal organic salt is selected from the groupconsisting of n-butyric acid, α-methyl butyric acid, iso-valerie acid,2-ethyl butyric acid, 2,2-dimethyl butyric acid, 3,3-dimethyl butyricacid, 2,3-dimethyl butyric acid, 3-methyl pentanoic-acid, 4-methylpentanoic acid, 2-ethyl pentanoic acid, 3-ethyl pentanoic acid,2,2-dimethyl pentanoic acid, 3,3-dimethyl pentanoic acid, 2,3-dimethylpentanoic acid, 2-ethyl hexanoic acid, and 3-ethyl hexanoic acid.
 8. Theprocess of claim 1, wherein the silica sol liquid further comprises aβ-diketone.
 9. The process of claim 1, wherein the silica sol liquidfurther comprises an organic solvent selected from the group consistingof an ester, an alcohol, a ketone and a hydrocarbon.
 10. The process ofclaim 1, wherein the partial hydrolyzate of an alkoxysilane oligomer isobtained by hydrolyzing one or more silane compounds having at least onealkoxy group.
 11. The process of claim 10, wherein the alkoxysilaneoligomer is selected from the group consisting of tetraethoxysilane,tetrapropoxysilane, methyltriethoxysilane, dimethylmethoxysilane,phenyltriethoxysilane, chlorotrimethylsilane, vinyltriethoxysilane, andaminopropyltriethoxysilane.
 12. The process of claim 1, wherein thesilica sol liquid comprises from 0.5 to 10 wt. % of metal content basedon an oxide.
 13. The process of claim 1, wherein the crucible coatedwith the silica sol liquid is heated at a temperature of from 600 to1,000° C., for 10-120 minutes.
 14. A quartz glass crucible, comprising atransparent coated layer, wherein said coated layer comprises acrystallization accelerator dispersed in a silica matrix on at least aportion of an inside and/or an outside surface of said crucible.
 15. Thequartz glass crucible according to claim 14, wherein said crucible isobtained by coating a silica sol liquid comprising a metal salt and apartial hydrolyzate of an alkoxysilane oligomer on the surface of thecrucible, and heating the crucible coated with silica sol liquid to forma transparent coated layer comprising a crystallization acceleratorderived from said metal salt.
 16. The quartz glass crucible according toclaim 14, obtained by coating the crucible with a silica sol liquidcomprising a metal organic acid salt or a metal carbonate of one or moreof magnesium, calcium, strontium, or barium, on the surface of thecrucible, and heating said coated silica sol liquid to form atransparent coated layer comprising the metal oxide or the metalcarbonate as a crystallization accelerator.
 17. The quartz glasscrucible according to claim 14 wherein the crucible is used for pullingup silicon single crystal.